Spin-current-driven thermoelectric coating

Kirihara, Akihiro; Uchida, K.; Kajiwara, Y.; Ishida, Masahiko; Nakamura, Y.; Manako, T.; Saitoh, Eiji; Yorozu, Shinichi

doi:10.1038/nmat3360

Cited by 263 publications

(250 citation statements)

References 30 publications

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“…1(a)]. Films below ∼90 nm show an increase of the signal amplitude with increasing thickness, in agreement with observations for polycrystalline Bi-substituted YIG [28]. For the epitaxial pure YIG films, we find for larger thicknesses a decreasing slope, leading to a saturation of the signal.…”

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Length Scale of the Spin Seebeck Effect

et al. 2015

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We investigate the origin of the spin Seebeck effect in yttrium iron garnet (YIG) samples for film thicknesses from 20 nm to 50 μm at room temperature and 50 K. Our results reveal a characteristic increase of the longitudinal spin Seebeck effect amplitude with the thickness of the insulating ferrimagnetic YIG, which levels off at a critical thickness that increases with decreasing temperature. The observed behavior cannot be explained as an interface effect or by variations of the material parameters. Comparison to numerical simulations of thermal magnonic spin currents yields qualitative agreement for the thickness dependence resulting from the finite magnon propagation length. This allows us to trace the origin of the observed signals to genuine bulk magnonic spin currents due to the spin Seebeck effect ruling out an interface origin and allowing us to gauge the reach of thermally excited magnons in this system for different temperatures. At low temperature, even quantitative agreement with the simulations is found. The thermal excitation of a spin current by a temperature gradient is commonly called the spin Seebeck effect (SSE) which is detected by the inverse spin Hall effect (ISHE) [1,2], leading to a thermovoltage similar to the charge analogue, the Seebeck effect. Experimental evidence of the SSE, first in ferromagnetic metals [3], and later, both in semiconductors [4] and in insulators [5][6][7][8], has brought up the question about the origin of the SSE. Of particular interest for spin caloritronics is the observation of the SSE in insulators, which allows us to generate pure spin currents in insulating systems.However, the underlying mechanism, properties, and the origin of the observed signals have been highly controversial. Thermally induced magnonic spin currents have been suggested as the origin [9,10], based on the presence of the effect in magnetic insulators, which excludes charge currents as the source. Despite this explanation of the origin of the effect, direct experimental evidence has not been reported. While parasitic interface effects [11] were suggested as an alternative source of the SSE due to a polarization of the paramagnetic detector layer [12], generally, the observed effects are now primarily attributed to magnonic spin currents [13,14].Time resolved experiments trying to address the problem by probing the temporal evolution of the SSE have obtained contradictory results: For film thickness up to 61 nm, no cut-off frequency due to an intrinsic limitation by the SSE was observed [15]. In contrast, for μm thick films, a characteristic rise time was found, and a finite magnon propagation length of the order of several 100 nm was put forward as a possible explanation [16,17]. This clearly calls for study to reveal the origin of this discrepancy as it underlies the fundamental mechanism of the SSE and to determine the intrinsic length scale.To clarify the origin of the measured SSE signals, we present a detailed study of the relevant length scales of the longitudinal SSE (LSSE) coveri...

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confidence: 89%

Length Scale of the Spin Seebeck Effect

et al. 2015

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“…The spin Seebeck effect provides another way to overcome the Wiedemann-Franz law; in the spin Seebeck device, the heat and charge currents flow in different parts of the sample: κ is the thermal conductivity of the magnetic insulator, and ρ is the electrical resistivity of Figure 14. Concept of the STE coating based on the spin Seebeck effect [12]. The STE coating exhibits a straightforward scaling: a larger film area leads to a larger thermoelectric output.…”

Section: Thermoelectric Coating Based On the Spin Seebeck Effectmentioning

confidence: 99%

Theory of the spin Seebeck effect

et al. 2013

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Abstract. The spin Seebeck effect refers to the generation of a spin voltage caused by a temperature gradient in a ferromagnet, which enables the thermal injection of spin currents from the ferromagnet into an attached nonmagnetic metal over a macroscopic scale of several millimeters. The inverse spin Hall effect converts the injected spin current into a transverse charge voltage, thereby producing electromotive force as in the conventional charge Seebeck device. Recent theoretical and experimental efforts have shown that the magnon and phonon degrees of freedom play crucial roles in the spin Seebeck effect. In this article, we present the theoretical basis for understanding the spin Seebeck effect and briefly discuss other thermal spin effects.

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“…The experimental geometry, having paths for heat and electric currents independent and perpendicular to each other, allows to have two different materials that can be optimised independently and it is also advantageous for the implementation of thin film devices over large surfaces, for example, simply by thin film coating. 32 Moreover, the observation of the SSE in magnetic insulators implies the potential to generate pure spin currents with lesser dissipation losses due to mobile charge carriers and further expanding the range of possible materials where spin mediated thermoelectric conversion can be studied. However, a main disadvantage of the SSE is the low magnitude of the thermoelectric output.…”

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Thermoelectric performance of spin Seebeck effect in Fe₃O₄/Pt-based thin film heterostructures

et al. 2016

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We report a systematic study on the thermoelectric performance of spin Seebeck devices based on Fe 3 O 4 /Pt junction systems. We explore two types of device geometries: a spin Hall thermopile and spin Seebeck multilayer structures. The spin Hall thermopile increases the sensitivity of the spin Seebeck effect, while the increase in the sample internal resistance has a detrimental effect on the output power. We found that the spin Seebeck multilayers can overcome this limitation since the multilayers exhibit the enhancement of the thermoelectric voltage and the reduction of the internal resistance simultaneously, therefore resulting in significant power enhancement. This result demonstrates that the multilayer structures are useful for improving the thermoelectric performance of the spin Seebeck effect.

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Spin-current-driven thermoelectric coating

Cited by 263 publications

References 30 publications

Length Scale of the Spin Seebeck Effect

Length Scale of the Spin Seebeck Effect

Theory of the spin Seebeck effect

Thermoelectric performance of spin Seebeck effect in Fe₃O₄/Pt-based thin film heterostructures

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Spin-current-driven thermoelectric coating

Cited by 263 publications

References 30 publications

Length Scale of the Spin Seebeck Effect

Length Scale of the Spin Seebeck Effect

Theory of the spin Seebeck effect

Thermoelectric performance of spin Seebeck effect in Fe3O4/Pt-based thin film heterostructures

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Product

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Thermoelectric performance of spin Seebeck effect in Fe₃O₄/Pt-based thin film heterostructures